If one of your suppliers (manufacturers) charges a handling fee for orders, you can pass that fee on to your customers.
Order  | Type  | Name  | Expression  | Rate Expression  | Surcharge Expression  | 
10  | Reference  | HasManufacturer  | Product.ProductManufacturers.Any  | 
  | 
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20  | Reference  | hasManufacturerX  | [@HasManufacturer](Manufacturer.Name = "X")  | 
  | 
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50  | Decimal  | SurchargeForX  | Items.Any([@hasManufacturerX]) ? 10 : 0  | 
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100  | Option  | Shipping  | true  | Shipping.Fedex  | [SurchargeForX]  | 
Additionally, you can show the customer a description explaining that a fee has been added (it appears to customer under the shipping option name). Just include a Description Expression on the Option line:
[SurchargeForX] = 0 ? "" : "A $" + [Surcharge].ToString() + " has been added because your cart contains a product from manufacturer X"
If you only want to charge the fee if the total amount of merchandise from that particular manufacturer is under $250, then we need to calculate the total $ amount of the items for that manufacturer, and then the expression for SurchargeForX would need to check if that total less than $250:
Modify the above - add line 30 for the total $ calculation and change line 50 to use the total:
Order  | Type  | Name  | Expression  | Rate Expression  | Surcharge Expression  | 
…  | 
  | 
  | 
  | 
  | 
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30  | Decimal  | TotalForX  | Items.Where([@hasManufacturerX]) .Sum(Product.Price * Quantity)  | 
  | 
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50  | Decimal  | SurchargeForX  | [TotalForX] < 250 ? 10 : 0  | 
  | 
  | 
Note, that the “the total amount of merchandise from that particular manufacturer” is the full price amount – i.e. does not include any discounts.
(Updated Aug. 2014.  If using nopCommerce versions prior to 3.00, then use ProductVariant.Product in plasce of just Product, and ProductVariant.Price in place of Product.Price)